A TOF mass spectrometer can be employed to determine the mass-to-charge ratio of ions based on the time required for the ions to travel through a field free region to reach a detector. In practice, the resolution of a TOF spectrometer can be limited by a variety of factors, such as the initial positional distribution of ions along the TOF axis, the kinetic energy spread of ions as they enter the TOF spectrometer, and the length of field free region, among others. Although a number of advances have been made in improving the resolution of TOF spectrometers, there is still a need for further improvements.